Slowdown of nonequilibrium dynamics in gapped `qubit' chains

TL;DR

This paper analytically investigates the nonequilibrium relaxation dynamics of anisotropic XY spin chains, revealing long-lived entangled states with diverging relaxation times due to quantum interference, relevant for quantum computation.

Contribution

It provides an analytical solution for the relaxation dynamics of inhomogeneous initial states in infinite qubit chains, identifying long-lived entangled excitations with diverging relaxation times.

Findings

Universal relaxation driven by quantum fluctuations.

Existence of long-lived, entangled excitations.

Diverging relaxation times at degenerate stationary points.

Abstract

We solve the nonequilibrium dynamics of qubits or quantum spin chains (s=1/2) modeled by an anisotropic XY Hamiltonian, when the initial condition is prepared as a spatially inhomogeneous state of the magnetization. Infinite systems are studied analytically, yielding a universal relaxation driven by quantum fluctuations. Particular long-lived excitations are found, for which the relaxation time diverges as a consequence of constructive quantum interference at degenerate stationary points. Those states are intrinsically entangled and may be of interest for performing quantum computation. We also numerically analyze finite samples to assess the extent of size effects.